Great input peterc. Yeah I'm now down to engine sound as the main reason for 50i. I think I've lost interest in the 40d and its between the 50:s.

But I don't know if engine sound alone can motivate twice the gas bill

Do you know if there are any other differences between the m50d and others more than side mirrors, air intakes instead of fog lights and larger brake discs? Is there any difference in suspension, driveline etc from 50i?